Multispectrum analysis of the nu(9) band of (C2H6)-C-12: Positions, intensities, self- and N-2-broadened half-width coefficients

摘要

Line positions, intensities, Lorentz self- and N-2-broadened half-width coefficients have been measured for (P)Q(3), (P)Q(2), (P)Q(1), (R)Q(0), (R)Q(1), (R)Q(2), and (R)Q(3) sub-band transitions in the nu(9) fundamental band of (C2H6)-C-12. A multispectrum nonlinear least-squares fitting technique was used to fit up to 17 high-resolution (similar to 0.00156 cm(-1)), room temperature absorption spectra of pure (99.99% chemical purity) natural sample of ethane and lean mixtures of the high-purity ethane diluted with N-2. A Bruker IFS 120HR Fourier transform spectrometer located at the Pacific Northwest National Laboratory (PNNL), in Richland, Washington was used to record the data. A standard Voigt line shape was assumed to fit all the data since no line mixing or other non Voigt line shapes were required to fit any of the spectra used in the analysis. Short spectral intervals (similar to 2-2.5 cm(-1)) of all 17 spectra covering a specific (P)Q or (R)Q sub-band were fit simultaneously. For the first time in an ethane band, pressure-broadened half-width coefficients were determined for the torsional-split components. However, for better reliability of the retrieved coefficients for the weaker components (transitions with large intensity ratios of 4:1 or 3:1 for most K levels between the strong and weak components), constraints were used such that the half-width coefficients of both torsional-split components for a given J were identical for a specific broadening gas. No pressure-induced shift coefficients were necessary to fit the spectra to their noise level. The present study revealed for the first time the dependence of self- and N-2-broadened half-width coefficients upon the J, K quantum numbers of the transitions in ethane. A number of transitions belonging to the nu(9)+nu(4)-nu(4) and the nu(9)+2 nu(4)-2 nu(4) hot bands were also observed in the fitted regions and measurements were made when possible.